# ============================================================================
#  http://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx_11.html
# ============================================================================
#
# SYNOPSIS
#
#   AX_CXX_COMPILE_STDCXX_11([ext|noext])
#
# DESCRIPTION
#
#   Check for baseline language coverage in the compiler for the C++11
#   standard; if necessary, add switches to CXXFLAGS to enable support.
#   Errors out if no mode that supports C++11 baseline syntax can be found.
#   The argument, if specified, indicates whether you insist on an extended
#   mode (e.g. -std=gnu++11) or a strict conformance mode (e.g. -std=c++11).
#   If neither is specified, you get whatever works, with preference for an
#   extended mode.
#
# LICENSE
#
#   Copyright (c) 2008 Benjamin Kosnik <bkoz@redhat.com>
#   Copyright (c) 2012 Zack Weinberg <zackw@panix.com>
#
#   Copying and distribution of this file, with or without modification, are
#   permitted in any medium without royalty provided the copyright notice
#   and this notice are preserved. This file is offered as-is, without any
#   warranty.

#serial 1

m4_define([_AX_CXX_COMPILE_STDCXX_11_testbody], [
  template <typename T>
      struct check
          {
	        static_assert(sizeof(int) <= sizeof(T), "not big enough");
		    };

    typedef check<check<bool>> right_angle_brackets;

    int a;
        decltype(a) b;

    typedef check<int> check_type;
        check_type c;
	    check_type&& cr = static_cast<check_type&&>(c);
	    ])

AC_DEFUN([AX_CXX_COMPILE_STDCXX_11], [dnl
  m4_if([$1], [], [],
          [$1], [ext], [],
	          [$1], [noext], [],
		          [m4_fatal([invalid argument `$1' to AX_CXX_COMPILE_STDCXX_11])])dnl
			    AC_LANG_ASSERT([C++])dnl
			      ac_success=no
			        AC_CACHE_CHECK(whether $CXX supports C++11 features by default,
				  ax_cv_cxx_compile_cxx11,
				    [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
				        [ax_cv_cxx_compile_cxx11=yes],
					    [ax_cv_cxx_compile_cxx11=no])])
					      if test x$ax_cv_cxx_compile_cxx11 = xyes; then
					          ac_success=yes
						    fi

  m4_if([$1], [noext], [], [dnl
    if test x$ac_success = xno; then
        for switch in -std=gnu++11 -std=gnu++0x; do
	      cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx11_$switch])
	            AC_CACHE_CHECK(whether $CXX supports C++11 features with $switch,
		                         $cachevar,
					         [ac_save_CXXFLAGS="$CXXFLAGS"
						          CXXFLAGS="$CXXFLAGS $switch"
							           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
								             [eval $cachevar=yes],
									               [eval $cachevar=no])
										                CXXFLAGS="$ac_save_CXXFLAGS"])
												      if eval test x\$$cachevar = xyes; then
												              CXXFLAGS="$CXXFLAGS $switch"
													              ac_success=yes
														              break
															            fi
																        done
																	  fi])

  m4_if([$1], [ext], [], [dnl
    if test x$ac_success = xno; then
        for switch in -std=c++11 -std=c++0x; do
	      cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx11_$switch])
	            AC_CACHE_CHECK(whether $CXX supports C++11 features with $switch,
		                         $cachevar,
					         [ac_save_CXXFLAGS="$CXXFLAGS"
						          CXXFLAGS="$CXXFLAGS $switch"
							           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_11_testbody])],
								             [eval $cachevar=yes],
									               [eval $cachevar=no])
										                CXXFLAGS="$ac_save_CXXFLAGS"])
												      if eval test x\$$cachevar = xyes; then
												              CXXFLAGS="$CXXFLAGS $switch"
													              ac_success=yes
														              break
															            fi
																        done
																	  fi])

  if test x$ac_success = xno; then
      AC_MSG_ERROR([*** A compiler with support for C++11 language features is required.])
        fi
	])
